cis-specific living polymerization of 1,3-butadiene with CoCl2 and methylaluminoxane

The polymerization of 1,3-butadiene was conducted by CoCl2 combined with methylaluminoxane (MAO) as a cocatalyst at 0 and 18degreesC. The uni-modal molecular weight distribution curves of the resulting polymers shifted toward higher molecular weight regions and became narrower when increasing the polymerization time. The number-average molecular weight increased linearly with polymerization time, while the polymer yield increased exponentially in the initial stage. As a consequence, the number of polymer chains, calculated from the polymer yield and (M) over bar (n), increased gradually with polymerization time to reach a plateau value. These phenomena was interpreted based on a slow initiation system without any termination and chain transfer reaction. The microstructure of the polymer was determined by H-1 NMR and C-13 NMR spectroscopy to be a cis-1,4 structure in a 98-99% purity.